This invention is primarily directed to an improved stationary combustion apparatus designed to utilize solid fuel such as household and industrial waste, it will be understood that any of various types of combustible, particulate materials may serve as the supply fuel feed for the instant apparatus. The term xe2x80x9cmass fuelxe2x80x9d referred to herein, is intended to mean any matter being combusted while resting on a surface or traveling on or along a surface. This might be distinguished from methods in which the matter is purposefully suspended in air a substantial distance above a surface. It might also be distinguished from methods, which require the matter to be fragmented before combustion. Mass fuel applications which this invention may be utilized include, but are not limited to elastomeric products, coal, waste coal, sewage sludge, biomass products, municipal solid waste, industrial waste, infectious waste, and manure. Generally, this invention relates to combustion systems which may be utilized as an apparatus and method for the combustion of mass fuel. Specifically, the invention is intended to provide an improved technique for efficiently combusting a mass fuel, possibly having widely varying combustion characteristics, upon a grate assembly in an incinerator or furnace. The combustion system is designed specifically to be an improvement over current incinerator or combustion grate assemblies and current methods of combusting a mass fuel.
The difficulty of burning certain mass fuels such as refuse is well known. Refuse often includes a high percentage of slow-burning or wet materials, which can impede combustion and exhibit an erratic burn rate. Furthermore, such compositions can vary continuously with the weather, season, area where collected, conditions under which stored and other uncontrollable and unpredictable variables.
One known method of burning or combusting refuse incorporates the use of a combustion grate for supporting the fuel during combustion. The method can be directed at dividing the combustion grate into two or three separate treatment zones and, through plenum or supply chambers, may provide combustion air under differing parameters to each one, varying the characteristics of the air to suit the combustion needs. Thus, the air in the first zone containing fresh, un-burned refuse may be heated to dry out the trapped moisture, with combustion possibly not commencing until the refuse has entered the next zone, which may be supplied with a different air mix. The control of combustion in various zones has sometimes been thought to be limited to varying the characteristics of the air flowing to each zone. However, as the thickness of the refuse layer and its combustion characteristics may not be uniform across any one zone, burning time may be longer, possibly dictated by the slowest burning area on the grate.
It can, therefore, be desirable to divide the grate surface into additional zones and to provide independent control of the combustion in each zone to maximize combustion efficiency. Furthermore, the control could optimally be as automatic as possible, so that each zone can be monitored and adjusted continuously, in an effort to maximize the efficiency of the burning to obtain the greatest throughput of fuel. In regard to combustion efficiency, the throughput of fuel may include the disposal through combustion of an input feed material, and or in the alternative, the production of a source of energy, such as heated air, water or steam from the burning operation.
Optimal burn or combustion efficiency may be achieved by simultaneously mixing or agitating the mass fuels and burning or combustion. Although the simultaneous steps of agitating and combusting of mass fuels may have been previously performed in prior combustion techniques, the overall objective of agitating and combusting may be performed in a variety of systems to further optimize combustion efficiency. In particular, it can be desirable to provide a means for mixing or agitating the fuel in specific ways during the combustion process. The result can be such that the overall combustion efficiency is improved.
One system often available for performing mass fuel agitation prior to the present invention appears to provide a stepped combustion grate, whereby a part or all of the steps move in a fashion which apparently aids in the overall mixing and travel of the fuel in a predominant direction. However, it may be desirable to provide a combustion system that incorporates less mechanical complexity than a moving grate system to possibly enhance the economics of the system as well as the throughput or combustion efficiency.
A system to accomplish the mixing or agitation of mass fuel may provide combustion air being fed through the grate assembly as the source of agitation. However, the use of combustion air for the dual purpose of combustion and agitation presents additional problems of system optimization. The use of one controlled air source for combustion as well as fuel agitation may not allow for the optimization of either the combustion or the agitation. In particular, the system may maintain the required combustion air flow to support the overall combustion process. However, the specific requirements needed for the agitation may be neglected. Similarly, the system may maintain the requirements needed to perform the agitation of the fuel. However, the necessary requirements for the proper oxygen-to-fuel ratio for combustion may be neglected either with too much or too little air. Combined with the possible need to adjust to varying fuel combustion characteristics in many instances, the ability to efficiently perform both the task of combustion air supply and fuel agitation with one air source is hampered. Therefore, it is desirable to accomplish both efficient combustion air supply and fuel agitation in a mass fuel combustion system to provide improvement in the overall system efficiency.
One system in particular, previously developed and patented as U.S. Pat. Nos. 4,955,296 and 5,044,288 by the inventor of the present invention, and hereby incorporated by reference, discloses an apparatus and method for the combustion of mass fuel incorporating a stationary grate plate assembly in the combustion system. The system may include an inclined assembly with perforated support tubes for the introduction of agitation air at particular locations along the stepped grate assembly. Combustion and agitation may occur at separate treatment zones along the grate surface in a controlled manner. Although excellent in its addressing of the problems intended, even the above referenced designs can be improved upon. They may not have provided as efficient an introduction source for combustion air and agitation air to the grate assembly as is now possible. System throughput or efficiency may be further enhanced in a system for introducing the combustion air and agitation air by optimized introduction defined by the particular grate plates.
Furthermore, the above referenced patents may also not have optimally provided for the efficient control of combustion parameters apart from combustion air and mix air control. Other system parameters may be monitored and controlled to further enhance the combustion efficiency. It would be desirable, then, to monitor and control the combustion system based upon system parameters, such as, by way of example and not of limitation, combustion chamber temperature, oxygen content of chamber air, carbon monoxide content of chamber air, and mass fuel feed rate, among others. Furthermore, the use of combusted air from the process may be used to further enhance system parameters such as, again by way of example and not of limitation, recycled air for combustion chamber temperature control. System parameters may further be optimized by a particular coordination of air introduction within the combustion system. It is desirable, therefore, to provide a combustion system that can monitor and control combustion parameters of the system and can optimize the parameters through the efficient use and introduction of multiple air sources.
Additionally, agglomerated combustion by-product or perhaps even slag may form within combustion systems resulting from the spent or combusted mass fuel accumulating within the system. A need, therefore, may exist to efficiently remove agglomerated combustion by-product within the system to optimize the throughput of as yet uncombusted fuel or otherwise.
The present invention provides a combustion system that addresses the inadequacies that may have existed with prior incineration or combustion systems. Accordingly, the present invention provides a mass fuel combustion furnace and methods for combusting a mass fuel.
It is an object, therefore, of the present invention to provide an improved combustion system for combusting a mass fuel. In particular, it is an object of the present invention to provide a combustion system for combusting a mass fuel that improves the speed of response and flexibility in the control of combustion of mass fuels. A goal of the present invention therefore can be to provide a combustion system that injects a secondary agitation gas into the fuel mass which can lift, agitate, dry and control the migration of the fuel during the combustion process.
It may be a further an object of the present invention to provide a combustion system for combusting a mass fuel without the need for or degree of mechanical movement typically associated with the grate assembly. A goal of the present invention therefore is to provide a combustion system that allows the grate to be xe2x80x9cstationaryxe2x80x9d to a large degree.
It can be a further object of the present invention to provide a combustion system for combusting a mass fuel without adversely affecting the combustion process. A goal of the present invention therefore is to provide a combustion system that limits the addition of significant excess oxygen, such as atmospheric air in the fuel introduction system.
Yet another object of the present invention may be to provide a combustion system for combusting a mass fuel that provides for agitation gas injection with a plurality of injection points and to independently control the rate of delivery of the gas flow at each point. A goal of the present invention therefore is to provide a combustion system with control of the velocity or flow of the mix gas at each point where it is released into the fuel and to provide a force available for performing the tasks of mixing, drying and controlling the migration rate of the material.
In particular, it may be an object of the present invention to provide a combustion system for combusting a mass fuel that enhances throughput and combustion efficiency in a system for introducing the combustion gas and agitation gas. A goal of the present invention therefore is to provide a combustion system that optimizes agitation gas introduction defined by the particular grate plates.
Still another object of the present invention is to provide a combustion system that minimizes variations in heat release rates during the combustion process. A goal of the present invention therefore is to provide a combustion system that controls the fuel feed rate to the combustion process.
It is further an object of the present invention to provide a combustion system for combusting a mass fuel that minimizes the effects of agglomerated combustion by-product during the combustion process that may discharge through the combustion grate. A goal of the present invention therefore is to provide a combustion system that efficiently provides for the removal of ash and agglomerated combustion by-product.
In particular, it is an object of one embodiment of the present invention to provide a combustion system for combusting a mass fuel that efficiently controls the overall combustion process using multiple parameters. A goal of the present invention therefore is to provide a combustion system that monitors and optimizes parameters within the system.
In particular, it may be an object of the present invention to provide a combustion system for combusting a mass fuel that provides a plurality of treatment zones for efficient combustion control and subsequent agglomerated combustion by-product removal. A goal of the present invention therefore is to provide a combustion system with multiple treatment zones, each zone having a separate introduction of combustion and agitation gases, independent rate control of delivery of combustion and agitation gas and separate agglomerated combustion by-product reduction method.
Another object of the present invention is to provide a combustion system for combusting a mass fuel that provides control of the temperatures on the combustion grate surface and throughout the combustion process. A goal of the present invention therefore is to provide a combustion system using exhaust gas, agitation gas and other types of control.
Other objects of the invention are disclosed throughout other areas of the specification and claims. In addition, the goals and objectives may apply either in dependent or independent fashion to a variety of other goals and objectives in a variety of embodiments.